This invention relates to a spectral light metering and mixing system for use in the production and reproduction of color photographs of all kinds, and also in color analyzing, metering and calibrating apparatus used in photographic, graphic, scientific, and other related disciplines. Almost without exception, state of the art spectrographic systems depend upon the so-called color triangle theory. This theory teaches that all colors of the visible spectrum lying roughly between 4000 and 7500 Angstrom Units can be produced by the use of the spectra of red, blue, and green, or alternately by the secondary or substractive colors of yellow, magenta, and cyan produced by mixing adjacent colors of the primary triangle. The color triangle spectra may be produced by three individual sources of appropriate frequencies, or it may be produced by absorption filters of appropriate hues exposed to the beam of a white light source of the appropriate spectrum. It may also be produced from a white light source of the appropriate spectrum by reflections from colored mirror surfaces or the bending of the light through colored prisms.
The operator of any of the various spectral devices designed about the primary color triangle or its alternate secondary form, must have a good working knowledge of color theory as well as technical knowledge related to the operation of the particular manual operated except when operating automatic equipment used in production-line photographic reproduction. Here, optical sensing devices are employed to determine the intensity and spectral distribution necessary to approximate a correct exposure. Such automatic equipment is large, complicated and expensive to acquire and maintain and is accident-prone. Such automatic equipment is confined almost exclusively to production line photo finishing plants catering to the popular snap-shot trade. The order of color accuracy of the automatic equipment is too low for commercial or professional requirements and such equipment is generally not suited for the making of various different size enlargements.
In operation of all state of the art spectrographic equipment utilizing color absorption filters other than automatic equipment, the operator must manually establish a spectral balance between all three colors of the triangle. He may introduce either no filter, a single filter, or a combination of any two at his discretion. All three filters cannot be introduced into the beam of white light at the same time as this would result in partial or total absorption of the light spectrum.
Substantially all of the color analyzing equipment currently in use is actually a form of a densiometer which affords no visual preview of the proposed finished photograph, but simply presents galvanometer readings related to density curves. Such readings must be translated to the filter selection by the operator subject to his knowledge, skill and experience.
In operation of state of the art spectrographic apparatus, confusion can arise in the mind of even the skilled operator. This is especially true of photographic apparatus employing white light sources and absorption filters. The subtractive filter configuration which is commonly employed consists of yellow, magenta, and cyan filters. Since cyan is the opposite of the combined values of both yellow and magenta, that is, it absorbs both spectra, great care must be exercised when working in the cyan range. Each advance of the cyan filter can necessitate a corresponding increase of either yellow or magenta, yet at other times may not.
State of the art color analyzers of all existing types must be laborously "programmed" in advance of initial use, requiring the making of prior photographic test prints by guesswork to develop the program calibrations. Programs must be developed for various types of negatives and for each color programed into the apparatus. Should any variations occur anywhere along the total photographic reproductive chain, all the analyzer programs are rendered useless, necessitating the reestablishment of the entire series of tests and programing. In any event, all programs are subject to gradual deterioration and eventual loss. Causes for the gradual decay and ultimate loss of all programs are these: Electronic drift caused by the absorption of moisture, aging of electronic components, deterioration of cathod ray tubes, etc. Chemical drift induced by oxidation, constant depletion and replacement of the various processing chemicals by replenishment. Temperature drift of the analyzer, the photographic paper and the chemistry.
Over and beyond the gradual drifts, abrupt changes can totally nullify the analyzer programs. Such changes as replacement of components, introduction of new paper emulsions, complete replacement of the photographic chemistry due to aging or accidental contamination, etc.
Probably the greatest deficiency of all state of the art analyzers, regardless of costs and expense of operation is the total lack of follow-up capabilities. If the final photograph is faulty, it is not possible to re-analyze the results and apply further correction. Such further corrections must be accomplished by the eyes of a skilled color technician working with hand-held viewing filters and personal judgment.
These and other problems were not satisfactorially resolved until the emergence of the instant invention.